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Tons of dross with my new Spectrum 375

11-12-2006, 05:56 PM

Can someone diagnose what I'm doing wrong?... I just got a new Spectrum 375 plasma cutter, and it's running on 240v. No matter what I cut, 16ga on up to 3/16" I get tons of dross on the bottom of the cut. It's very difficult to remove. I have tried changing the output, from 16 amps all the way to full power 27amps with no effect. I have tried increasing the air pressure, even outside the little green arrows. I have also tried slowing my cut, and increasing the speed of the cut to the point at which it doesn't cut all the way through 1/8" steel. Seems that no matter what I do, I end up with tons of dross, or it doesn't cut all the way through. Also - I get a lot of curved lines on the cut, no smooth edges. This is very disappointing seeing that this machine is rated to cut 3/8" and I'm getting crappy cuts on 1/8". I'm doing just small cuts (an inch or two) with a 25 gallon compressor set at 90psi. I'm totally disappointed and wondering A) am I doing something totally wrong, or B) is my machine defective?

The manual says to turn the machine on, and set the power output knob to gas/air set. It then says to set the air pressure with the air control knob. When I do this, as soon as I get the pressure to the minimum area of the green arrows, it sputters air and sounds like a machine gun. The only way I can properly set the air pressure is to do exactly what the directions say NOT to do, and set the air pressure after I have set the output to the desired amperage.

I'm beginning to wonder if I got the lemon of the lot (as usual) or if I'm just not using the machine correctly.... There are so few directions, and I keep trying all kinds of different settings with amperage and air settings, but I keep getting lots of very difficult to remove bottom dross and not-so-nice cuts.

Chop it and ride it,
Tim

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Lincoln SP135T
Miller Spectrum 375

Comment

I have had some dross on thicker pieces but was easily knocked off. Also changed the way I hold and move the torch. I watched a Miller Rap get a clean cut on 1/2 and he held the torch just off the piece when he started and kept it pointed STRAIGHT DOWN. If ya run the torch at an angle you are forcing it to make a cut thicker then the material actually is. Of course on 1/8" it shouldn't matter.

What have you done to dry the air going into the 375?

At the moment we are only using a Motor Guard Filter to dry the air and it seems to be working as we put a Dessicant Indicator between the filter and cutter to give us a visual on moisture getting in.

Also what is the CFM rating of your compresser at 90 PSI?

I know the 375 requires 4.5 CFM @ 60 PSI according to Page 10 of the Manual. They usually show two ratings on a compressor, one at 40 PSI and the other at 90 PSI. I am running mine on a 60 Gal Compr putting out 10.3 CFM @ 90 PSI.

Again these are just things to check. Also if all else is good, try changing a tip/electrode. When I noticed cuts getting a little rough, I switched tips and that made a big difference. The first tip I am sure we beat to death cutting up everything we found into tiny little pieces.

We put a self propelled 22" lawn mover in a shoe box.

Comment

The manual says to turn the machine on, and set the power output knob to gas/air set. It then says to set the air pressure with the air control knob. When I do this, as soon as I get the pressure to the minimum area of the green arrows, it sputters air and sounds like a machine gun.

The reason it sputters there is not enough AIR getting to the 375 from the compressor.

STOP HERE

OK ... when it begins to sputter it is not getting enough flow from the compressor. Crank up the compressor.

You need to have at least 4.5CFM@60 PSI going into the 375 for the Air Regultor on the 375 to work.

Comment

My compressor is a 25 gallon and I have the regulator set at 90psi. My compressor is under powered (less than 4.5 cfm @ 90psi) but the Miller rep told me I would be ok, just not able to do real long cuts without having the compressor running constantly. Also, there are a lot of guys here saying they have run the 375 on pancake compressors which have less output than my 25 gallon. If I set the air pressure on the 375 even way over the green arrows I still get heavy dross.

Something doesn't sound right here. I'm starting to lean towards thinking I have a bad 375...

Comment

What size & length hose are you using from your compressor to the 375?
It sounds like you've got pressure, but low volume.
There's not a table leg or a wheel on the hose, limiting flow is there?

I was thinking the same thing at first but was able to duplicate his problem with unimpeded flow by setting up the 375, making a cut, and then turning back the Regulator on the 375. If he has enough pressure in and cranks the regulator on the 375 up, the problem should go away. If not then it is a FLOW issue

Although I still think an increase in flow rate would be better. Sometimes just increasing the hose size is a help. I used to run skinny hose, now it is all the larger diameter and the air tools seem to operate better.

Comment

Where should the pressure be on the 375? I have cranked it up way past the little green arrows that seem to indicate a desired pressure range. Even this has not helped. I'm really at a loss here. Cutting 1/8" to 3/16" should be child's play for this machine, but it is really doing a crappy job of it.

Chop it and ride it,
Tim

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Lincoln SP135T
Miller Spectrum 375

Comment

Call Miller & ask them what you need to do...If it's the machine, they'll fix it.
If it's you...They'll do what they can to help fix that also!
They WANT you to be happy with your machine....Give them a call.
There should be a toll-free number in your manual....
HTH

Professional Auto Mechanic since 1974
My own shop since 1981
Cya Frank